Another "vote" for Affinity Photo v.1.7.0 breaking the old Nik Collection (system: MacOS El Capitan, 10.11.6). I reinstalled Affinity Photo 1.6.11 using the "replace" option in MacOS. Although the right side of the Affinity Photo window seems to have some "left over" from v.1.7.0.
The old Nik Collection is now functional again.
On a side note, based on my few experiments with v.1.7.0, it seemed slower than v.1.6.11. Image adjustments (including Nik) and exporting were/are faster in v.1.6.11 than I encountered with v.1.7.0. The Nik situation aside, it seems strange that Serif would issue an update/upgrade that is slower than the previous version.
And for those considering Nik Collection 2, here is some info on DxO's "philosophy". I am also a user of DxO PhotoLab (previously just DxO) as part of my Raw processing. I have been receiving emails from DxO about Nik Collection 2 and their "special" offer of only $100 for this new version. The offer includes the ESSENTIAL ("Lite") version of PhotoLab; I have the ELITE version. As far as DxO is concerned, it does not matter - you get no discount even if you have another DxO product.
So I plan to be satisfied with Affinity Photo v.1.6.11 and the old Nik Collection. Between DxO and Serif, I see no need to go any farther.